1. Field of the Invention
The present invention relates generally to a file backup technique, and more specifically relates to a technique applicable and effective for backup technique of files which are accessed and updated by a plurality of clients in a device enabling a plurality of clients to access to files and storage regions via a network, such as NAS (Network Attached Storage, hereinafter referred to simply as “NAS”) or a file server.
2. Description of the Related Art
In backup of a file with a conventional NAS or file server, if a file is used by a plurality of clients during its update when backup of the file is being conducted, data of the file to be backed up is retrieved as being in an unfixed state. Thus, in order to retrieve backup of the file as being closed and fixed, it is necessary for the respective clients to temporarily stop access to the file to be backed up for backup, and permit the clients to re-access to the file after the backup.
It is to be noted that Japanese Patent Application Laid-open Publication No. 5-265829 discloses a technique to maintain identity of replicas without the need of communication between a server and a replica server by means of monitoring communication between a client and a server on the LAN by the replica server and then updating the replica by taking in information from the client to the server.
Further, Japanese Patent Application Laid-open Publication No. 7-210430 discloses a technique for backup by defining the position and size of the file to be backed up and the position and capacity of backup medium, relating the former information with the latter information, and selecting a suitable medium subsequently.
Further, Japanese Patent Application Laid-open Publication No. 10-91505 discloses a technique enabling file sharing between workstations in a network environment including a plurality of workstations which do not have shared disks by configuring information of an original file name of a file to be backed up and a backup destination.
In a conventional NAS or file server, a file used in NAS or a file server was accessed by multiple clients to share information and it was difficult to identify which client was accessing to the file at the time of backup during actual use. In this situation, it is very difficult to realize a method where all clients are requested to temporarily stop accessing to the file to be backed up, and then be notified of accessibility to the file after completing backup.
Further, in the techniques disclosed in the above-mentioned Japanese Patent Publications, technical problems as described above regarding backup of files in a storage apparatus shared on a network are not appreciated.